Where does furnace get combustion air?

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What is the purpose of cold air return vents?

The Purpose of Your Cold Air Returns

The return registers draw stale air into the ductwork, where it’s pulled through the filter to capture dust and debris and then delivered back to the HVAC equipment for reconditioning.

What is a combustion air vent?

What is combustion air? Combustion air is a source of oxygen needed to burn fuel such as natural gas or liquid propane (LP). You can’t produce a flame in a furnace without proper combustion air. The image above shows the combustion air as a vent in the garage to pull air from the attic.

Does air come out of a cold air return?

Simply put, a cold air vent returns cold air back into the furnace. No furnace can adequately operate without sufficient return air supply. We can think of a furnace as lungs. It ‘breaths out’ hot and it ‘inhales’ cold air.

What happens when there is not enough combustion air?

Lack of adequate combustion air causes improper heater operation, increased maintenance cost, and risks dangerous production of carbon monoxide gas.

Where must the combustion air opening be located?

One of these openings must be located within the top 12 inches of the appliance space, and one opening must be located within the bottom 12 inches of the appliance space. The minimum dimension of each opening is 3 inches. Figure 4. Figure 4: Two permanent openings must be sized and located correctly.

Are cold air returns connected to furnace?

When warm air is delivered to a room, the existing cold air in that room is pushed into the cold air returns. Once inside your cold air returns, that air travels through your ductwork back to your furnace where it is filtered, heated and sent back to warm your home.

What happens if cold air return is blocked?

In the heating cycle, blocked cold air returns can cause the heat exchanger inside the blower compartment to store too much heat and eventually crack. If the cracks are too large, the furnace can emit carbon monoxide into your home’s air.

Is it OK to block a return vent?

It’s important not to block your return air vent because your HVAC system needs constant return air to work properly. Blocked air return ducts will cause your system to lose energy efficiency and cause premature failure of your HVAC system. This does not mean you don’t have many options for hiding your return air vent.

Are cold air return vents necessary?

Cold air return vents aren’t the most elegant feature in your home, but they exist for reason. These vents, commonly found in hallways or on ceilings, are absolutely essential to an air conditioner’s well-being. Cold air returns take in warm air from your home’s indoor spaces for use in your air conditioning system.

Where should cold air returns go?

Cold air returns are located on interior walls in a home, typically close to the floor or low on the wall. You want to make sure that cold air return vents are not blocked or covered by furniture so that your home can get proper air circulation.

Why are there two vents in my room?

If you have a central air system, you know there are a lot of ducts running through your home. These ducts carry air to and from your heating and cooling system. In order for air to enter and exit the ducts, multiple vents are needed.

How much combustion air does a furnace need?

A furnace must be supplied a specific amount of fresh air per cubic foot of gas burned. To burn 1 cubic foot of gas, approximately 1,000 Btu for natural gas, requires 10 cubic feet of air for perfect combustion (Figure 2).

Can combustion air be taken from a bedroom?

Combustion air shall not be obtained from an area in which flammable vapors present a hazard. Fuel-fired appliances shall not obtain combustion air from any of the following rooms or spaces: 1. Sleeping rooms.

How close can a cold air return be to the furnace?

Returns must be min. 10ft from furnace and cannot be located in a small volume space. See the IRC for the simple formula. Supply and returns must be sized for the space and balanced.

Why do I have two air returns?

Having two air return vents allows you to seasonally control which air is returning to the HVAC system. In older homes, this may not be an option. The theory is that in the Summer cooling season, you want to be circulating warmer air back through the HVAC system to be cooled.

Can you put something in front of a cold air return?

Home Inspection Insider explains that an air return vent needs 6-12 inches of space in front of it, and recommends that you do not put large, bulky furniture like couches and bookshelves in front of an air return vent.

Does a high efficiency furnace need a cold air return?

Since high efficiency furnaces draw air directly from outside, the furnace itself does not require a fresh air intake in order to replace inside air that otherwise would have been drawn from the room the furnace is located in.

Why does my furnace have 2 vents?

High-efficiency furnaces use sidewall vents for “breathing” in outside air for fuel combustion, and “exhaling” cooled exhaust gases nearly depleted of heat.

Do all HVAC systems have fresh air intake?

The HVAC system does not mechanically bring fresh air into a building. However, cracks and leaks in the HVAC ducts can allow exterior air to come indoors, so it is essential to regularly service your HVAC system to ensure that all filters are working properly and that there are no inefficiencies in the transfer of air.